Method of making a multitrack magnetic head employing double helix structure

ABSTRACT

A multitrack magnetic head is made from an electrically conductive first helix formed on an iron wire that is, in turn, wound to form a second helix. By longitudinally cutting along one side of the second helix, the first helix is severed into respective coils on discrete gapped cores.

This is a division of application Ser. No. 82,847, filed Oct. 9, 1979now U.S. Pat. No. 4,314,298 issued Feb. 2, 1982.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to multitrack magnetic heads and tomethods and parts for forming such heads.

2. Description Relative to the Prior Art

In the art of magnetic recording, there is a trend toward the use ofmultitrack magnetic heads having large numbers of cores per unit widthacross the head surface that interacts with the recording medium. Oneexplanation for this trend may be found in the fact that a plurality ofhead cores can record a specific amount of data at an informationwriting speed which is only about ##EQU1## of the information writingspeed which would be required when writing with only one core. Forexample, for a playback gap length of, say, 100μ" (μ"=microinch), abandwidth of 2 mHz would necessitate a single core writing speed of 200inches per second (ips) if use of the recording medium is to beoptimized. By contrast (still using playback gap lengths of 100μ"), thatsame bandwidth of 2 mHz can be written by a 500-track record head at arelative head-to-medium speed of only 0.4 ips ##EQU2## Such recording ofa large bandwidth in a large number of tracks at low writing speedsuggests, among other things, the linear tape recording of videoinformation. Linear tape recording of video information, as opposed tothe recording techniques employed in helical scan and quadruplex videorecorders, implies a simplification of hardware: not only does alessened information writing speed relax the mechanical demands of therecording operation, but head switching, rotary head drums and variouselectronics are obviated, as well.

Perhaps the most common technique for forming a multitrack magnetic headis that which is shown generally in U.S. Pat. No. 4,084,199. Such atechnique is characterized by the respective winding of coils ondiscrete cores, and the positioning of the coil-supporting cores in thinslots in a head block. Because of the tedium inherent in the windingcoils on tiny cores, and because of the brittleness associated with theslotting of the head block, a head made according to the teaching ofU.S. Pat. No. 4,084,199 is generally limited to about 30 tracks perwidthwise inch of the recording medium. In an attempt to increase thenumber and density of discrete cores in a multitrack magnetic head,various head manufacturing techniques employing photolithography havebeen suggested, thereby to avoid the need for discrete coil winding andto avoid the requirement for sawing thin slots in a head block. U.S.Pat. Nos. 3,893,189 and 3,983,622 are representative of such techniques.

While photolithography and similar techniques hold promise for futuredevelopments in the art of multitrack magnetic heads, it must, however,be realized that such techniques have limited versatility when it comesto providing multitrack magnetic heads of varying design. It would, forexample, be desirable to have a multitrack magnetic head which is suchthat, when made from a basic core material, variations in the resultanthead design can be provided relatively easily, and without ado. In otherwords, were it desired, for example, to provide a multitrack magnetichead of N cores with M turns per core, or a multitrack magnetic head ofX cores with Y turns per core, such could be provided handily from thesame basic core material.

SUMMARY OF THE INVENTION

In accordance with the present invention, a double helix core-and-coilstructure is provided, the preselectable length of such double helixcore-and-coil structure determining the number of cores which are to beemployed in a head constructed from such core-and-coil structure. Onehelix of the double helix core-and-coil structure constitutes anelectrically conductive coil wrapped on a length of magnetic wire; andwhich magnetic wire is, itself, helically wound to form the second helixof the double helix core-and-coil structure. By longitudinally cuttingthrough one side of the double helix core-and-coil structure, asuccession of gapped cores is provided; and by judiciously contactingthe electrically conductive helix, supported by the magnetic helix, at apredetermined arc of the magnetic helix, the number of turns of thecoils in question may be selected. (The term "gap", as used herein, doesnot necessarily mean "transducer gap". Rather, "gap" shall beinterpreted to mean any break in an otherwise continuous form, and whichbreak may or may not constitute a "transducer gap".)

It will be appreciated that a magnetic head made by the techniquedisclosed herein will comprise coils which extend virtually the fullextent of their supporting cores, despite the fact that (perhaps) only apreselected number of turns of such coils are electrically active.

The invention will be described with reference to the figures, wherein:

FIG. 1 is a side view showing one helix of the double helixcore-and-coil structure;

FIG. 2 is a side view showing the double helix core-and-coil structure;

FIGS. 3a, 3b and 3c are respectively plan, edge and side views ofapparatus employed in the practice of the invention;

FIG. 4 is an edge view, like that of FIG. 3b, but showing a gap-formingcut in the double helix core-and-coil structure;

FIGS. 5a and 5b are edge views like that of FIG. 3b, but showing,respectively, the removal of a mandrel employed as part of the head andgap-forming processes;

FIGS. 6a and 6b are, respectively, edge and under views illustratingadditional procedures for forming a gap line in a multitrack magnetichead embodying the invention;

FIGS. 7 and 8a and 8b are views useful in describing the manner in whichelectrical contact is made to the electrically conductive helix of thedouble helix core-and-coil structure;

FIGS. 9 and 10 are side elevational views showing how a multitrackmagnetic head embodying the invention may be finished;

FIG. 11 is an edge view useful in describing a presently preferredtechnique for forming a gap in a multitrack magnetic head according tothe invention;

FIGS. 12a, 12b and 12c are, respectively, edge, side elevational andschematic perspective views which relate to the showing of FIG. 11 andwhich are useful in describing the invention; and

FIGS. 13 through 16 are illustrations which respectively correspond tothe illustrations of FIGS. 7 through 10.

A multitrack magnetic head having 252 coil-wound cores per widthwiseinch of the head, and which head embodies the invention, will now bedescribed in terms of its method of manufacture:

Referring to FIG. 1, a very fine insulation-covered copper wire 10(0.0009 inch in diameter) is helically wound into a coil along and aboutthe length of an iron wire 12 (0.002 inch in diameter). Then, asdepicted in FIG. 2, the coil-supporting iron wire 12 is, itself,helically wound on a mandrel 14, thereby forming the basic double helixcore-and-coil structure. (It will be appreciated that the double helixcore-and-coil structure may be provided, and stocked, in large spoolsand/or skeins thereof, whereby multitrack heads of various numbers ofcores may be provided, depending upon the length of the double helixcore-and-coil structure which is employed.) The mandrel 14, which inthis case has a circular cross-section of 0.022 inch in diameter, and iscoated with a mold release material, is then laid along the length of agroove 16 in a non-magnetic jig 18. See FIGS. 3a, 3b and 3c. After thedouble helix core-and-coil structure is bonded in place in the groove 16by epoxy 19, a longitudinal cut 20 (see FIG. 4) is made into the doublehelix core-and-coil structure, thereby cutting the jig in half andpermitting it to be folded (at least partially), as in FIG. 5a; thiscauses the mandrel to "mold-release" and to pop free of the double helixcore-and-coil structure.

Using the double helix core-and-coil structure (10, 12) as a hinge, thetwo pieces 18a and 18b of the jig are positioned (see FIG. 5b) so as toplace the cut edges 20a, b in a common plane. The edges 20a, b are thenlapped flat and thereafter coated with an extremely thin coat (about 1micron in thickness) of aluminum oxide 22 (or the like), the aluminumoxide serving as a gap spacer for the head under construction.

Now, as depicted in FIG. 6a, the jig parts 18a, b are swung back andpositioned so that the edges 20a, b face each other with the gap spaceraluminum oxide therebetween, such positioning causing the cross-sectionof the double helix core-and-coil structure (10, 12) to collapse into agenerally elliptical form. As best illustrated in FIG. 6b, the jig parts18a, b (before, after or during the time they are swung back intoposition) are relatively shifted longitudinally of the double helixcore-and-coil structure by an amount related to the pitch of the ironwire helix, whereby the cut helical iron wire (12) gets converted into asuccession of substantially planar, untwisted, cores having respectivegaps (i.e., high reluctance discontinuities) therein. With the jig partsso positioned, a non-magnetic block 23 (see FIG. 7) having a groove 24is so bonded to the structure of FIGS. 6a and 6b that the unsupportedpart 26 of the double helix core-and-coil structure (10, 12) resides inand along the length of the groove 24. After an insulation-coveredcopper wire 28 is threaded through the center of the double helixcore-and-coil structure, thereby to serve as a common bias lead for thecores of the head under construction, epoxy is employed to hold the wire28 in place and to fill the voids of the groove 24 and of the doublehelix core-and-coil structure.

Because of the very nature of the double helix core-and-coil structure,electrical contact to the coils formed from the helically woundelectrically conductive wire 10 may be made, simply, by lapping thestructure of FIG. 7 to the lap lines 30a, b. While such lappingtriangulates (FIG. 8a) the cross-section of the head under construction,it conveniently forms aligned apertures through which rows of coppercontact points 32 are exposed on each of two opposing sides of the head;and which contact points comprise respective parts of the double helixcore-and-coil structure (10, 12). See FIG. 8b. Leads from ribbon cablesare then soldered respectively to the rows of copper contact points. (Itwill be appreciated that, although it will be usual to bring leads toall of the copper points 32, it will be possible to vary the number anddensity of the active cores of the head by selectively bonding leads todifferent ones of the contact points 32. For example, if it is desiredto provide a 126-track head, instead of a 252-track head, every otherlead of the ribbon cables is simply left opened.)

In finishing off the head, block pieces 36a, b and 38a, b are secured(FIG. 9) to the triangular block of FIG. 8a, the block pieces 38a, bbeing provided with channels 40a, b through which the leads (42a, b) maypass. Then, finally, the head is contoured as in FIG. 10 to place thegap line 44 at the head surface which is disposed to contact therecording medium.

Whereas the number of discrete cores in a head made as described abovedepends upon the length of the double helix core-and-coil structurewhich is employed, the number of turns on each of the cores depends onthe lap angle employed to expose the copper contact points 32, asindicated in connection with FIG. 7.

Although a transducer gap(s) formed by the head manufacturing techniquedescribed above is useful for many purposes, the provision of a highprecision gap to optical tolerances is dependent on the ability of theiron wire 12 to sustain and withstand precision lapping. And, it will beappreciated, the life of such a gap is directly related to and dependentupon the (small) diameter of the iron wire 12 which is used. To improveon the quality and life of a head gap embodied in a multitrack magnetichead according to the invention, the teaching of FIGS. 1 through 10above may be modified slightly as illustrated in connection with FIGS.11 through 16: After the double helix core-and-coil structure has beenlongitudinally cut, as was taught in connection with FIG. 4, and themandrel 14 popped free as in FIG. 5a, a pre-formed pole tip piece 50(FIG. 11) approximating the dimensions of the cut 20 is placed inpressing relation between the core edges 20a, b. The pole tip piece 50,which is best depicted in the perspective showing of FIG. 12c, ispreferably formed from a stack of ferrite pieces 52 interspersed withand bonded to ceramic pieces 54, the stack being longitudinally halved,lapped and reformed with a high reluctance gap spacer 56 between thehalves. After placing the pole tip piece 50 between the core edges 20a,b (still referring to FIG. 11), the jig pieces 18a, b are swung back(FIG. 12a) while (or before, or after) longitudinally shifting the jigpieces 18a, b (see FIG. 12b) by an amount substantially equal to thepitch of the iron wire helix, as was done above regarding FIG. 6b.Thereafter, as depicted in connection with FIGS. 13 through 16, themultitrack head under construction is provided with coil and bias leads;and is contoured, essentially as was described above in connection withFIGS. 7 through 10. (The parts of FIGS. 13 through 16 havingcorresponding parts in FIGS. 7 through 10 are identified with the same,but primed or double-primed, character notations.)

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. A method for use in the making of a multitrackmagnetic head, said method comprising the steps of:(a) longitudinallycutting one side of a double helix core-and-coil structure formed of asubstantially helical coil of electrically conductive wire wound on andabout a helix of magnetic material, thereby to form a row of discretecoil-wound gapped cores, (b) supporting said row of cores in a jig, and(c) removing parts of said jig to form first and second rows ofelectrical contacts for the coils on said cores,whereby electrical leadsmay be brought to said contacts to activate electrically said coils. 2.The method of claim 1 including the additional step of longitudinallyshifting respective parts of said cores to remove the respectivesubstantially helical twists thereof.
 3. The method of claim 1 includingthe additional step of placing a pole tip piece, comprised of magneticmaterial sandwiching a high reluctance material, between the gaps ofsaid coil-wound cores.
 4. A process for use in making a multitrackmagnetic head comprising the steps of:(a) winding an electrical wiresubstantially helically along and about a length of magnetic material,(b) forming said length of magnetic material with said electrical wirethereon into a substantially helical form thereof, and (c) cutting oneside of said helical form of magnetic material so as to sever thehelically wound electrical wire into discrete coils on discretehelically twisted sections of magnetic material,said discrete sectionsof magnetic material constituting the individual cores of saidmultitrack magnetic head.
 5. The process of claim 4 including theadditional step of removing the helical twists of the cores formed fromsaid cut magnetic material.
 6. The process of claim 4 including theadditional step of placing a pole tip piece, comprised of a pair ofmagnetic structures sandwiching a high reluctance material, within thecut which is made to one side of said helix of magnetic material.
 7. Amethod of forming cores for use in magnetic heads comprising the step ofcutting a coiled length of magnetic material along one side thereof,said magnetic material having an electrical wire wrapped generally alongits length, thereby to sever the magnetic material into a plurality ofdiscrete cores having respective coils thereon.
 8. A method for use informing a multitrack magnetic head comprising:(a) substantiallyhelically winding electrical wire along a length of magnetic wire, (b)substantially helically winding the magnetic wire having the electricalwire thereon on an elongated mandrel, (c) placing the wire-supportingmandrel in a jig, and (d) cutting, in the direction of the longitudinalaxis of said mandrel, the length of said magnetic wire while said wireis on said mandrel to sever the magnetic and electrical wire into aplurality of discrete coil-wound cores.
 9. The method of claim 8including the additional step of removing said mandrel after said lengthof magnetic wire is cut.
 10. The method of claim 9 including theadditional step of applying gap space material to the severedcross-sections of the coil wound cores after said mandrel has beenremoved.
 11. The method of claim 8 wherein said jig is such that, whensaid length of magnetic wire is cut, said jig is halved, and wherebysaid jig halves may be oriented for additional processing of the coreswhich are formed.
 12. The method of claim 11 including the additionalstep of relatively shifting the jig halves to remove substantially thehelical twists in said cores.
 13. The process of claim 8 including theadditional step of lapping said jig to expose respective parts of thecoils on said discrete cores.